On-ramp signals

Current RTA focus

RTA supports the installation of North Carolina’s first freeway on-ramp signals to relieve rush hour congestion along a segment of I-540 westbound in northwest Raleigh.

“On-ramp signals,” also known as “ramp metering signals,” “ramp meters,” “ramp signals,” or “flow signals,” can help freeways remain free-flowing by regulating the flow of traffic entering the freeway during periods when the freeway mainline approaches congested conditions.

About on-ramp signals

In the absence of freeway on-ramp signals, a long line of waiting vehicles can enter a crowded freeway at once and potentially create a backup on the freeway main lanes. While on-ramp signals cannot absolutely guarantee free-flow travel, they can provide a degree of protection by minimizing or delaying the onset of congestion for that freeway segment.

An on-ramp signal is located on the ramp between the intersecting street and the freeway. When activated, the on-ramp signal alternates between short red and green displays. The intermittent displays of a short red signal throttles the demand at the end of the ramp so that the freeway is better able to accept the entering vehicles and remain free-flowing.

On-ramp signals operate on a part-time basis, with the focus on providing congestion relief during rush hour periods. The vast majority of the day the signals are dark and the on-ramp functions normally.

On-ramp signals can preserve freeway flow at a very low cost compared to new construction. With traffic entering the freeway in a smoother, regulated fashion, everyone can arrive to their destinations sooner, more reliably, and with increased safety. In addition, the Federal Highway Administration has noted that on-ramp signals can lead to a reduction in fuel consumption and vehicle emissions. Click here for information from Washington State DOT.

Results of independent study of on-ramp signals

When on-ramp signals were temporarily deactivated on several Minneapolis-St. Paul freeways in response to a Minnesota legislative mandate, an independent study found that when on-ramp signals were deactivated:

Travel times increased 22%

Speeds dropped 7%

Travel time reliability decreased 91%

Crashes increased 26%, with a variation of 8% to 200% increase depending on crash type

Volume served by the freeway reduced 9%

In other words — all of the above delay, reliability, and safety measures were worse without on-ramp signals in place.